In cutting tools, indexable inserts for instance, chip runoff surfaces in the form of specially shaped chip-runoff areas serve in the main to ensure that in the chip-removing formation there is a good chip runoff without endangering operating personnel and without the chips causing destruction of the cutting edge. The essential requirements for chip-runoff areas are to produce as good a chip deformation and as good a chip break as possible over as wide a range of different cutting requirements as possible and, at the same time, to meet the requirement (in essence, the opposite requirement) that the cutting forces additionally appearing because of the chip deformation be kept limited, since higher cutting forces generally involve a rise in temperature of the cutting edge and result in a shortened service life.
In order that the mechanical strength of the cutting edge not be reduced too greatly by the chip-runoff areas, thereby making it necessary to accept a premature end to the service life of the cutting tool, because of cutting-edge breakages, a tried and proven way has long been to provide between the cutting edge and the chip-runoff areas a rotating bezel having a constant or a variable breadth, rather than to have the chip-runoff areas begin directly at the cutting edge.
West German Offenlegungsschrift No. 2,515,686 discloses a cutting tool in which the chip area is furnished with several indentations or grooves which are separated from each other and are disposed at a certain distance from the cutting edge. The grooves run preferably perpendicular to the cutting edge and reduce, according to the teaching set forth therein, the runoff chip's contact surface with the chip area, whereby the friction, and therefore the occurring temperature load on the cutting edge, is reduced. However, the grooves have no influence on chip deformation and chip break, so that this cutting tool exhibits only limited advantages in comparison with previously known designs.
In West German Offenlegungsschrift No. 2,545,769 there is disclosed an adjustable cutting tip of the kind mentioned hereinabove. However, the hollows are constructed preferably in the shape of a spherical segment or with a cross-section in the shape of a circular segment. At least one hollow is disposed preferably within the region of the transition from the major cutting edge to the minor cutting edge. A disadvantage of the construction disclosed is that the notches, viewed in the chip-runoff direction, have an ascending rear side and as the chips run off they are deformed excessively by the ascending rear side and an overbreak of the chips occurs, especially when large forward feeds are delivered to the cutting edges. Consequently, high cutting forces as well as an excessively great temperature development on the cutting edge results. Moreover, by locating at least one hollow in the transitional area between the major cutting edge and the minor cutting edge, a mechanical weakening of the cutting edge results, especially at the areas thereof which are subjected to the higher mechanical and thermal stresses. Therefore, this design does not fulfill adequately the requirements mentioned above for chip-conducting steps.
There exists, therefore, a need for a cutting tool which does not exhibit the mentioned disadvantages and it is an object of this invention to provide a cutting tool of the kind described at the outset, which exhibits an improved chip runoff in comparison with known designs over as large as possible a range of different cutting requirements, and, at the same time, in comparison with known designs of chip-runoff areas, a reduction of the cutting forces and cutting temperature with consequent increase in service life of the cutting edge being attained. The present invention fulfills such a need.